This application is based on application Ser. No. 11-373810, filed in Japan on Dec. 28, 1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an air intake amount control apparatus for an engine, capable of controlling the intake amount of air supplied to the engine by means of a throttle valve which is driven to rotate by a motor.
2. Description of the Prior Art
In general, an internal combustion engine mounted on a vehicle is equipped with a throttle valve in an air intake path which is opened and closed in conjunction with a manipulation of an accelerator pedal by a vehicle driver. As a result, the amount of air sucked into the engine is controlled in accordance with the quantity of manipulation of the accelerator pedal.
Such an air intake amount control operation may be achieved by jointly coupling the throttle valve to the accelerator pedal by way of a mechanical coupling such as a link mechanism, a cable or the like.
However, the air intake amount control using such a mechanical coupling is suffered from the following problems. That is, the relationship between the push amount or the amount of depression of the accelerator pedal and the throttle opening degree is uniquely determined without any degree of freedom. Also, since the positional relationship between the accelerator pedal and the throttle valve is limited, freedom in mounting the mechanical coupling member on the vehicle is reduced.
Very recently, the need of freely controlling engine power is increasing for the purposes of improving an air intake amount control device for a gasoline direct injection type engine in which gasoline is directly injected into cylinders of the engine, also of improving stability in maneuverability of the vehicle as well as the sensation in acceleration. To fulfil such a need, an electronically controlled throttle device that is actualized by using a so-called xe2x80x9cDrive By Wirexe2x80x9d technique may constitute one of the most effective air intake amount control devices.
The electronically controlled throttle device is designed to control a throttle valve by using the xe2x80x9cDrive By Wirexe2x80x9d technique while discarding the use of the above-mentioned accelerator cable, the amount of depression of the accelerator pedal is electrically detected so that the throttle valve is accordingly driven to move by the motor. As a result, the throttle valve can be operated independent of the driver""s accelerator pedal manipulation, thus allowing the engine power to be controlled freely.
In a gasoline direct-injection type engine, an air-to-fuel ratio is changed over a wide range from a stoichiometric air-to-fuel ratio (stoichiometric A/F ratio) up to an ultra lean (ultra lean A/F ratio). However, there is a large difference between the torque produced during a stoichiometric A/F ratio drive operation and the torque produced during a ultra lean A/F ratio drive operation even at the same throttle opening degree. To suppress a torque variation occurring when the air-to-fuel ratio is switched between the ultra lean A/F ratio drive operation and the stoichiometric A/F ratio drive operation, the air intake amount is required to be corrected.
To solve these problems, an electronically controlled throttle device is employed.
Furthermore, Japanese Patent Application Laid-Open No. 5-240070, which was laid open to public in 1993, discloses a throttle valve control system capable of achieving a highly precise opening-degree control characteristic of a throttle valve by coupling the rotor of a brushless motor via a speed reducer or a reduction gear to the rotation shaft of the throttle valve.
Also, with this throttle valve control system, a counter electromotive voltage detector or a current switching detector is provided for detecting a counter electromotive voltage that is produced in the stator windings (hereinafter referred to as xe2x80x9cphasesxe2x80x9d) of the brushless motor when the phases of the brushless motor are switched from one to another. As a result, such an expensive high-precision rotary detector as referred to above can be omitted.
However, the above-mentioned conventional engine air intake amount control for controlling the throttle valve involves the following problems.
First, in order to switch the energizing phase of the brushless motor, either the counter electromotive voltage detector or the current detector is required, so that it becomes necessary to increase the signal input I/F of a motor control apparatus, thus resulting in high cost. Also, in the counter electromotive voltage detecting system, a counter electromotive voltage can be detected only when the brushless motor is rotating at a speed not less than a predetermined speed. Accordingly, it becomes difficult to detect the counter electromotive voltage in such a condition that the stationary/rotational operations are frequently repeated as in the throttle valve control.
Also, when the energizing phase is switched based on an output derived from a throttle sensor, there might occur a positional shift in the energizing phase switching positions caused by the allowances in the characteristics of the speed reducer and the throttle sensor.
Furthermore, in operation of the brushless motor, when a certain energizing phase is switched to a next energizing phase based on the output derived from the counter electromotive voltage detector or the current switching detector, the current is rapidly changed so that in cases where there is a shift or deviation in the output signal of any of the detectors with respect to a change in the magnetic flux applied to the phase, the torque produced by the motor becomes discontinuous. Thus, there arises a problem that the throttle opening degree is rapidly changed. As a result, a 3-phase energizing system may be employed in which the energizing currents having sine waves are respectively supplied to the U-phase, V-phase and W-phase, independently of each other. However, such a 3-phase energizing system has the following problem. That is, a detector capable of precisely measuring the rotation angle of the rotor of a motor is required.
As a consequence, the following energizing phase control system for the 3-phase windings is conceivable. In this control system, when a key switch is turned off, a brushless motor is driven stepwise so as to learn a geometric positional relationship between a rotor magnetic pole position and a stator based upon a sensor output signal of a throttle sensor; the resulting learned value is stored into a battery-backed-up memory such as a RAM and a non-volatile memory such as an EEPROM. When the key switch is turned on, a motor energizing phase angle at which a corresponding motor is energized is calculated based on both the output value of the throttle sensor and the rotor magnetic pole position learned value.
Let us consider the case where such a 3-phase winding energizing phase control system is applied to an actuator in which a throttle valve is held at an intermediate opening position when a motor for actuating the throttle valve is not energized. In this case, if a key switch is turned on to start the motor without previously performing the above-described rotor magnetic pole position learning operation after some component parts of the actuator have been replaced, then the rotor magnetic pole position learned value becomes unmatched with the actual rotor magnetic pole position of the actuator after the replacement of the actuator component parts. As a result, control on the throttle opening cannot be carried out by driving the motor. Thus, the engine is started with the throttle valve being opened and fixed at the intermediate opening position, and hence if the control apparatus cannot recognize this uncontrollable condition of the throttle valve, then there will result problems such as an abnormal increase in the engine revolution and the like.
The present invention is intended to obviate the aforementioned problems, and thus, has an object to provide an air intake amount control apparatus for an engine which is low in cost, and excellent in safety as well as controllability.
Bearing the above object in mind, according to the present invention, there is provided an air intake amount control apparatus for an engine comprising: a throttle valve mounted on a rotation shaft in an intake passage of the engine; a throttle sensor for sensing an opening degree of the throttle valve; a motor having a rotor coupled to the rotation shaft for driving the throttle valve based upon various sorts of engine operating information; a rotor magnetic pole position learning unit for driving the motor in a stepwise manner so as to learn a magnetic pole position of the rotor that is detected by the throttle sensor; a rotor magnetic pole position learned value storing unit for storing therein the magnetic pole position of the rotor learned by the rotor magnetic pole position learning unit as a magnetic pole position learned value; and a magnetic pole position identifying unit for driving the motor to a predetermined stepwise position so as to identify the magnetic pole position learned value stored in the rotor magnetic pole position learned value storing unit with the magnetic pole position of the motor at the predetermined stepwise position detected by the throttle sensor.
In a preferred form of the invention, a magnetic pole position learning operation of the rotor magnetic pole position learning unit is performed when a key switch is turned off.
In another preferred form of the invention, a magnetic pole position identifying operation of the rotor magnetic pole position identifying unit is performed when a key switch is turned on.
In a further preferred form of the invention, the air intake amount control apparatus for an engine further comprises an intermediate opening degree stopping mechanism for setting the opening position of the throttle valve to an intermediate opening degree position under such a condition that the motor is not energized when a key switch is turned on, wherein a magnetic pole position identifying operation of the rotor magnetic pole position identifying unit is carried out by driving the rotor in a stepwise manner from the intermediate opening degree position to a first rotor magnetic pole position learning position in a throttle fully-closed direction.
In a yet further preferred form of the invention, the rotor magnetic pole position identifying unit judges that the rotor magnetic pole position learned value stored in the rotor magnetic pole position learned value storing unit is not coincident with the magnetic pole position of the motor if a deviation between the rotor magnetic pole position learned value and the rotor magnetic pole position detected by the throttle sensor when the rotor is stepwise driven to a predetermined rotor magnetic pole position learning position upon turning on of a key switch is larger than, or equal to, a predetermined value.
In a further preferred form of the invention, when the rotor magnetic pole position identifying unit judges that the rotor magnetic pole position learned value is not coincident with the magnetic pole position of the motor detected by the throttle sensor, the rotor magnetic pole position identifying unit prohibits the execution of the throttle opening degree control operation until the key switch is turned off, judges that a position feedback failure happens to occur, gives a warning, and sets the throttle opening degree to the intermediate opening degree position.
In a further preferred form of the invention, a magnetic pole position identifying operation of the rotor magnetic pole position identifying unit is prohibited when a battery voltage is lower than, or equal to, a predetermined value.
In a further preferred form of the invention, a magnetic pole position identifying operation of the rotor magnetic pole position identifying unit is prohibited when the opening position of the throttle valve is without a predetermined range immediately after a key switch is turned on.
In a further preferred form of the invention, when the rotor magnetic pole position learning operation is not yet performed, the rotor magnetic pole position identifying unit prohibits the execution of the throttle opening degree control operation, prohibits the throttle opening degree control operation until the key switch is turned off, judges that a position feedback failure happens to occur, gives a warning, and sets the throttle opening degree to the intermediate opening degree position.
In a further preferred form of the invention, the rotor magnetic pole position learned value storing unit comprises: a volatile memory being energized by a battery to hold a storage operation; and a non-volatile memory. When a key switch is turned on with the battery having not been disconnected from the volatile memory, the rotor magnetic pole position identifying unit executes a rotor magnetic pole position identifying operation by using a magnetic pole position learned value stored in the volatile memory, whereas when the key switch is turned on just after the battery is disconnected from the volatile memory, the rotor magnetic pole position identifying unit executes a rotor magnetic pole position identifying operation by using the magnetic pole position learned value stored in the non-volatile memory.
In a further preferred form of the invention, the rotor magnetic pole position learning unit learns a fully-closed position of the throttle valve based upon the voltage value outputted from the throttle sensor when a voltage value outputted from the throttle sensor upon the rotor being stepwise driven from the throttle intermediate opening degree position in a throttle fully-closed direction is smaller than, or equal to, a predetermined voltage value, and when a deviation between a first voltage value outputted from the throttle sensor at a preceding stepwise position of the throttle valve and a second voltage value outputted from the throttle sensor at a present stepwise position of the throttle valve is smaller than, or equal to, a predetermined value.
In a further preferred form of the invention, the rotor magnetic pole position learning unit learns a fully-opened position of the throttle valve based upon the voltage value outputted from the throttle sensor when a voltage value outputted from the throttle sensor upon the rotor being stepwise driven from the throttle fully-closed opening degree position in a throttle fully-opened direction is greater than, or equal to, a predetermined voltage value, and when a deviation between a first voltage value outputted from the throttle sensor at a preceding stepwise position of the throttle valve and a second voltage value outputted from the throttle sensor at a present stepwise position of the throttle valve is smaller than, or equal to, a predetermined value.
In a further preferred form of the invention, when the throttle sensor detects either the fully-closed position or the fully-opened position of the throttle valve, the direction in which the rotor is stepwise driven is reversed by switching over energizing patterns.